Heretofore, leaf spring scales have been fabricated with a tandem construction so as to provide straight line motion, i.e. a substantially vertical deflection having little or no lateral play.
This type of construction can be seen with reference to Patent Nos:
2,105,514 (1971) GERMANY PA1 2,646,274 weckerly PA1 2,969,228 appius PA1 3,026,954 appius PA1 3,667,560 cooke
With the increasing demand for scales of higher and higher accuracies, it has been found that a significant distortion takes place in the spring rate of leaf spring scales of the above type. As the leaf springs deflect, they traverse a slight arc, that causes their effective bending lengths to be altered. This has the effect of changing the spring constant of the scale as the springs deflect. Where high accuracy is required, this distortion cannot be tolerated.
While it was known to prestress or prebend the springs to minimize these aberrations, a constant spring rate scale never has been achieved.
It has been found that by angling one spring portion of the multiple spring scale above the horizontal, and angling a corresponding spring portion along a horizontal axis, one deflection arc will be increasing at the same time the other deflecting arc is descreasing. If both spring portions are united about a common support, such that they act as a unitized spring, the bending length distortions in each spring portion will cancel each other throughout the deflecting range. This then, will have the effect of providing a total spring structure with a constant spring rate (an invarying spring constant throughout the weighing ranges).